Recently, with the rapid progress in portable and cordless appliances, there is a mounting demand for a secondary battery having a small size and light weight and having a high energy density that can be used as the power source of these appliances. In particular, based on the lithium secondary battery and nickel-hydrogen storage battery, many new products have been developed. Moreover, in the nickel-cadmium storage battery which is low in cost and high in reliability, further enhancement of its characteristics is desired.
A conventional nickel-cadmium battery is composed of a battery can, a plate group contained in the battery can, and an electrolytic member. The inner wall of the battery can is a smooth surface, so that the spiral plate group can be inserted easily. The plate group comprises a positive plate, a negative plate, and a separator. The plate group is spiral, and the negative plate is positioned on the outermost circumference, and this negative plate contacts with the inner wall of the battery can. That is, the battery can serves also as the negative terminal. The plate group is only wound, and the lead of the negative plate is not spot-welded or bonded to the bottom of the battery can. In this structure, therefore, since the inner wall of the battery can confronting the outermost circumference of the negative plate is a smooth surface, the negative plate and battery can only contact with each other, and the contact pressure is small, and hence the internal resistance of the battery is often increased. Moreover, the plate group is likely to be moved by an external impact, and the internal resistance is not stabilized. As a result, when the internal resistance is large, sufficient charging or discharging cannot be conducted.
To reduce the internal resistance of an alkaline manganese battery, in Japanese Patent Publication No. 7-99686, it is proposed to form fine vertical stripes on the inner surface of the can. However, in the case of the alkaline manganese battery in which the positive electrode compound directly contacts the inner surface of the can, it is effective to form vertical stripes at a protrusion height of 0.005 to 0.02 mm and a stripe pitch of 0.002 to 0.4 mm as disclosed therein. However, in the case of a battery in which contact between the negative plate and the inner wall of the battery can is desirably maintained only by inserting a spiral plate group, composed by winding a positive plate and a negative plate around a separator, into the battery can, a negative compound material having a high resistance value is interposed between the negative plate on the outermost circumference of the spiral plate group and the inner surface of the battery can. Accordingly, if the vertical stripe pitch is less than 0.4 mm, the contact surface area of both the battery can and the negative electrode material is increased, but the material resistance of the negative electrode material is high, and hence the effect for reducing the internal resistance of the battery and the effect for suppressing changes of internal resistance due to external impact are small.